U.S. Patent Application Publication No. 2010/0212656 and U.S. Pat. Nos. 6,739,136, 4,785,875, 4,753,072, 4,685,510, 4,671,064, 4,135,367, 4,010,018 disclose examples of different structures, designs and methods by which heat exchangers, Stirling engines, heat engines, and other engines function. Such systems often utilize a working fluid for transferring heat. Usually, such systems utilize a hot combustor exhaust gas to directly fire a hot side of the engine for transferring that heat and powering a device.
Small scale combustion, such as combustion that is used in heat engines to power underwater or space vehicles or small electric generators, often utilize small combustors that have significant design issues that prevent the combustors from operating efficiently. For instance, small combustors usually have large surface area to volume ratios, and thus have high parasitic heat loss. That is, the heat release rate varies approximately with the volume of the combustor while the heat loss from the combustor walls varies with the combustor surface area. A small scale combustor may thus have high parasitic heat loss as the heat lost through the combustor walls is usually transferred to the environment rather than a heat engine. As a result, the powering system's energy efficiency decreases. Coupling a small scale combustor with a Stirling engine presents a substantial design challenge as the exit temperature of the combustor must not be excessive or the hot side of the closed cycle heat engine will melt or otherwise deform from excessive thermal stresses that are limited by the material properties of the structures. This typically requires that excess diluents be introduced into the combustor or exhaust stream. For instance, burning kerosene with air may produce combustor exhaust temperatures well in excess of 3000° F. that would either melt or deform iron-based, cobalt-based, nickel-based, or chromium-based alloys and super alloys commonly used in the construction of a hot side of a closed cycle heat engine. Excess diluent must then be pumped into the combustor to prevent engine damage. The diluent is often excess air or exhaust products. The excess diluent presents two additional losses to the system efficiency as additional power or mechanical work is usually required to pump the diluents into the combustor and the diluent exits the hot side of the engine at a high temperature and represents an additional thermal loss to the system. In addition, since the required diluent mass and volume flow rates are usually many times that of the combustion products, the combustor must be made larger in order to accommodate the excess flow, which increases its weight and volume and further exacerbates the parasitic heat loss discussed above.
Prior art combustion devices for powering a closed-cycle heat engine, especially those for small power applications of about 5 kW or less of electrical power or shaft power, lose a significant fraction of the chemical power of combustion as heat loss through the combustor walls. This heat is ultimately transferred to the environment via a cooling jacket or insulation rather than powering the heat engine. Furthermore, piping the hot combustion gases to the heat engine is problematic if the exhaust gases are not tempered by dilution with either excess air or cooled exhaust products. These heat losses usually dictate that the combustor be designed as small as possible to reduce these parasitic losses, however, small combustors have short residence times that sometimes do not provide complete combustion or result in intermediate or frozen combustion products that lower the furnace efficiency of the thermal heat source.
A new design is needed that may improve the performance of engines and heat exchanges that such engines may be designed to drive or utilize. Such a design preferably permits a reduction in complexity in engine design while maximizing the thermal efficiency of the power system.